Materials Science and Engineering for the 1990s Maintaining Competitiveness in the Age of Materials (1989) / Chapter Skim
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4. Research Opportunities and the Elements of Materials Science and Engineering
4. Research Opportunities and the Elements of Materials Science and Engineering
Pages 110-140
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From page 110... ...
Other research topics may be linked to applications but may still not be adequately described by a breakdown of research opportunities according to materials function, because such topics may relate broadly to several, or all, of the functional classes of materials. An example is rapid solidification processing, which has already had important applications in metals for both structural and magnetic applications, and in ceramics for structural electronic applications.
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From page 111... ...
They have measured materials properties of all kinds, such as mechanical strength, optical reflectivity, and electrical conductivity. They have predicted and
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From page 112... ...
As discussed in Chapter 3, synthesis of new materials by unusual chemical routes and by various physical and chemical means has led to an era in which atom-by-atom fabrication can be achieved. Coincidentally, processing has received renewed attention, partly in response to challenges from international competitors who have reaped the benefits of improved quality and uniformity of traditional materials, and partly in response to the demands for process control to achieve the promise of advanced materials.
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From page 113... ...
Unique physical properties of polymers make possible diverse products such as sonar devices, liquid-crystal displays, electronic package encapsulation, and automobile interiors, but, conversely, the transport properties of polymers' constituents accelerate degradation, as illustrated by the "new car" smell present in newly assembled vehicles. In the broadest sense, materials properties represent the collective responses of materials to external stimuli; for instance, electrical or thermal conductivity are the measured result of the application of an electric field or temperature gradient.
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From page 114... ...
They also seek to understand how the materials properties are affected in service and how to predict and improve these changes in properties. The working environment is usually highly complex, involving multiple, often synergistic stimuli and forces, such as heat and mechanical stress cycling, moisture and oxidation exposure, and irradiation.
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From page 115... ...
In all real applications, many materials properties play roles in the design of a system. For example, in a relatively simple system such as an automobile hood, relevant properties include not only density, corrosion resistance, strength, stiffness, and forming and welding parameters, but also electrical conductivity (because of the possibility of radio frequency interference between engine devices and the antenna)
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From page 116... ...
The interaction between materials synthesis, materials performance, and component or equipment design is becoming increasingly sophisticated and complex. It is further complicated by the fact that current and future products increasingly call for intimate combinations of novel materials.
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117 Ct ~ iLN ~ ~ I ~ AIL 1 1 S o ~ of S _ 'a 0 of A; S ~ ._ .
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From page 118... ...
Concurrent with the development of techniques for characterizing the structure and composition of materials has been the development of analytical and modeling techniques to explain the origins of these observations, for example, quantum calculations to describe electronic structure and crystal structure stability; equilibrium and nonequilibrium thermodynamics to describe multiphase materials; and hydrodynamics and instability analysis to explain the development of microstructures in crystalizing metals and polymers. Historically, the development of materials has involved many key discoveries made at the macroscopic level (such as continuum behavior or mechanical properties)
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From page 119... ...
Studies of synthesis and processing have focused increasingly on the nanometer size regime, as is demonstrated by development of block copolymers, ultrafine ceramic powders, metallic microstructures, and superlattice electronic devices. The increased understanding of materials at this level has shifted the fundamentals of process control
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From page 120... ...
120 MATERIALS SCIENCE AND ENGINEERING FOR THE 1990s l FIGURE 4.4 Three slices of a three-dimensional icosahedral quasi-crystal. (Reprinted, by permission, from Paul Steinhardt.
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From page 121... ...
Synthesis and processing research is evolving to the point that, in some cases, new materials can be tailored, atom by atom, to achieve a desired set of properties or to obtain new and sometimes unexpected phenomena. Synthesis and processing encompass a comprehensive array of techniques and technologies as diverse as rolling of sheet steel, pressing and sintering of ceramic powders, ion implantation of silicon, creation of artificially structured materials, ladle-refining of steel, sol-gel production of fine ceramic powders, pouring of polymer-modified concrete, shaping by machining or chip processes, thermomechanical processing of alloys, preparation of polymers by chemical reactions, coating of turbine blades for corrosion resistance, zone refining of silicon, growth of gallium arsenide crystals, and laying-up of composite materials.
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From page 122... ...
....: ....... .~ ~ FIGURE 4.5 Monolithic substrate configurations developed as active components in catalytic converters.
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From page 123... ...
Notable examples in process technology include the markets for machine tools and semiconductor processing equipment. To ameliorate the flow of resources for manufacturing equipment to foreign markets, the United States needs to accelerate research on synthesis and processing equipment and to strengthen the manufacturing industry for this equipment.
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From page 124... ...
When coupled with process modeling and elements of artificial intelligence, these sensors promise to usher in a new era of intelligent processing of materials. Developments in this field will require the combined efforts of experts in sensor development, materials modeling, the relationships between process variables and product structure, and artificial intelligence (with a strong emphasis on expert systems)
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From page 125... ...
For example, the processes used for producing artificially structured materials make it possible to combine optically active materials with electronic circuitry in ways that should lead to qualitatively new kinds of optoelectronic devices. Artificially structured materials can be produced by a variety of techniques, including molecular beam epitaxy (MBE)
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From page 126... ...
An artificially structured material generally can be expected to exhibit novel and useful properties when the length scale of the structure is comparable to the characteristic length scale of the physical phenomenon of interest. Examples of interesting microscopic length scales include the de Broglie wavelengths of electrons, the wavelengths of phonons, the mean free paths of excitations, the range of correlations in disordered structures, characteristic diffusion distances, and the like.
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From page 127... ...
is obtained through the use of high-purity carbon steels with very low sulfur and phosphorus levels. Vacuum induction melting, vacuum arc remelting, and electron beam melting are used to obtain structural metals (especially superalloys and titanium)
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From page 128... ...
Today, important research topics on nucleation deal with how to avoid it to achieve high undercoolings and, hence, nonequilibrium structures in materials, and with how to promote it to achieve fine grain sizes. Topics in growth deal with interracial phenomena, dendritic growth mechanisms, nonequilibrium processes, and formation of heterogeneities such as lattice defects, segregation, porosity, and inclusions.
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From page 129... ...
A more detailed discussion of the promises of rapid solidification processing is given in Appendix B Rapid solidification technology has led to amorphous materials with new and useful combinations of magnetic properties.
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From page 130... ...
Figure 4.8, which shows an example of process fundamentals, illustrates the effects of substrate crystallography and beam direction on the microstructure of an electron beam weld. Consolidation processes include processing and manufacture of composite materials by a variety of techniques, especially pressing and sintering.
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From page 131... ...
Electrolytic Processing Electrolytic processing is an important segment of the broader, $28 billion electrochemical industry. The processing segment includes metal production, plating, semiconductor processing, and chemical production.
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directions of a single crystal Fe-~5Ni-~5Cr alloy, revealing the influence of beam direction and crystallography on the solidification substructure (original magnification: xS00, top; x 400, bottom)
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From page 133... ...
The cost of analytical instruments such as electron microscopes ranges from $50,000 to $850,000, and the cost of dedicated process equipment, such as MBE and ion implantation equipment, is in the range of $1 million to $2 million. Furthermore, these costs are rising rapidly, at well above the rate of inflation.
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From page 134... ...
This gradation in layer thickness results in gradations in those properties such as flow stress, hardness, corrosion resistance, magnetic properties, and wear resistance that depend on the layer thickness. (Courtesy National Institute of Standards and Technology.)
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From page 135... ...
In these same areas, national laboratories abroad also play a much more important role in instrument development than they do in the United States. A particular example from surface science is relevant.
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Notable examples include the markets for machine tools and semiconductor processing equipment. Yet a leading position in materials processing technology requires leadership capability in the machinery and equipment sector and a close collaboration with materials processing.
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Federal funding agencies have not made instrument development a prominent component of their programs. The Division of Materials Research at the NSF spends only about 1 percent about $1 million per year for the development of new instrumentation.
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From page 138... ...
The latter change has occurred in large part because instruments are now available to make highly detailed and quantitative measurements and because the computational ability exists to deal with the resulting wealth of data. Underlying all of these developments are advances in the theoretical understanding of materials properties and the mathematical ability to devise accurate numerical simulations.
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From page 139... ...
In the future, science-based numerical simulations in combination with new methods for storing, retrieving, and analyzing information may make it possible to optimize not only the properties of specific substances but also entire processes for turning raw materials into useful objects. Materials considerations are important throughout the life cycles of most products from design through manufacturing to support and maintenance and, finally, to disposal or recycling.
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From page 140... ...
The challenge is to give practitioners of materials science and engineering broad access to the increasingly expensive equipmentincluding major national facilities required to perform this characterization. · Unprecedented variability of materials properties is now available in new materials as a result of research in the areas of synthesis and processing and of properties, offering designers almost unlimited variability in design choices.
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